This invention relates to a brake noise preventing means used in disc brakes, more particularly to an improvement of a brake noise preventing means of the type wherein a plate member or members are inserted between the friction pad and the piston which urges the former.
In disc brakes of the kind in which a friction pad is urged into engagement with a rotating disc, by a piston reciprocating in an hydraulic cylinder, in order to stop or decellerate the rotation of the disc, unpleasant or disagreeable noises occur in not a few cases. Among these a noise named a squeal is the most unpleasant, and preventive attempts of the noise have long been done without attaining a perfect solution thereof.
An idea of inserting a plate member or members (hereinafter simply referred to as a shim or shims) between the friction pad and the piston for preventing or reducing this noise belongs to a series of attempts abovementioned, and U.S. Pat. No. 3,113,643, for example, is widely known as a representative invention for its excellent effect. This invention is characterized in that a so-called cut-out shim is inserted between the friction pad and the piston, which shim being partially cut out as an aperture (at a location wherein the inner end of the piston would normally abut the same on that side of the axis of the piston with which any given point on the disc first comes into alignment). Since then many disclosures have been made to improve the noise preventing effect by means of varying the size, location, and configuration of the cut-out portion of the shim or shims. A method of inserting a couple of so-called non-cut-out shims is also known. Further study of improving the noise preventing means of this type is, however, greatly needed to attain a better one.
For the purpose of better understanding of this invention a few of the recent examples will be cited hereunder: (a) inserting three laminated shims, i.e., three shims superposed one on the other with the central one having an aperture which contains lubricating grease therein (Japanese laid open Utility Model, numbered Sho-50-118382); (b) inserting two superposed shims, with one adjacent to the piston having a concaved groove facing the other shim on the friction pad side, in which groove lubricating grease is contained (Japanese laid open Utility Model, numbered Sho-50-118383); (c) inserting a shim, circular in shape and having a cut-out portion, so as to be pivoted on the friction pad wherein the pad abuts the piston for being able to vary the location of the cut-out portion (Japanese laid open Utility Model, numbered Sho-50-118388); and (d) inserting a shim tightly fixed to the backing plate of the friction pad for containing a lubricant, such as grease therein (Japanese laid open Utility Model Sho-50-142978).